332 FOODS AND DIETARIES 



phosphorus, have been recently found to aid the body in many of its most 

 important functions. The beating of the heart, the contraction of muscles, 

 and the ability of the nerves to do their work appear to be due to the pres- 

 ence of minute quantities of these salts in the body. 



Uses of Nutrients. The following table sums up the uses of 

 nutrients to man : 1 



Proteid Forms tissue (mus- 



White (albumen) of eggs, curd cles, tendon, and 



(casein) of milk, lean meat, probably fat), 



gluten of wheat, etc. 



Fats Form fatty tissue. 



Fat of meat, butter, olive oil, 

 oils of corn and wheat, etc. 



All serve as 

 fuel and yield 

 energy in form 

 of heat and mus- 

 cular strength. 



Carbohydrates Transformed into fat. 



Sugar, starch, etc. 

 Mineral matters (ash) .... Aid in forming bone, 



Phosphates of lime, potash, assist in digestion, etc. 



soda, etc. 



How the Exact Nutritive Value of Food has been Discovered. For 

 a number of years, experiments have been in progress in different parts 

 of the civilized world which have led to the beliefs regarding food just 

 quoted. One of the most accurate and important series of experiments 

 was made a few years ago by the late Professor W. O. Atwater of Wes- 

 leyan University, in cooperation with the United States Department of 

 Agriculture. By means of a machine called the respiration calorimeter 

 (Latin, color = heat + metrum = measure), which measures both the 

 products of respiration and the heat given off by the body, it has been 

 possible to determine accurately the value of different kinds of food, both 

 as fuel and as tissue builders. This respiration calorimeter is described 

 by Professor Atwater as follows : 



" Its main feature is a copper- walled chamber 7 feet long, 4 feet wide, 

 and 6 feet 4 inches high. This is fitted with devices for maintaining and 

 measuring a ventilating current of air, for sampling and analyzing this air, 

 for removing and measuring the heat given off within the chamber, and 

 for passing food and other articles in and out. It is furnished with a fold- 

 ing bed, chair, and table, with scales and appliances for muscular work, 

 and has telephone connection with the outside. Here the subject stays 

 for a period of from three to twelve days, during which time, careful 

 analyses and measurements are made of all material which enters the 

 body in the food, and of that which leaves it in the breath and excreta. 



1 W. O. Atwater, Principles of Nutrition and Nutritive Value of Food, U.S. De- 

 partment of Agriculture, 1902. 



